The instant invention relates to a fuel system for an internal combustion engine, and more particularly to a supplemental gaseous fuel system for a diesel engine.
Diesel engines, and more particularly stationary diesel engines, i.e., those powering generators, pumps, and compressor power units have heretofore been known in the art. A stationary diesel engine normally includes a load sensitive speed control system which automatically controls a diesel fuel supply to provide a precise volume of diesel fuel to the engine to yield a given power output. The speed control is therefore operative for automatically increasing or decreasing the volume of fuel flow in response to fluctuations in engine load. For example, a diesel electric generator is required to operate at a constant speed regardless of changes in load (known as transients) in order to produce electric power at a constant, predetermined frequency, i.e., 60 hertz. In this regard, the speed control automatically-increases or decreases the fuel flow in order to maintain the engine at a constant speed.
For reasons which may include fuel cost, availability of fuel, and engine exhaust emissions control, it has been known in the art to substitute a gaseous fuel, i.e., natural gas, propane gas, etc., for a predetermined percentage of diesel fuel consumed by the engine at a given power output. The use of diesel fuel in these diesel/gaseous fuel systems is typically limited at a minimum, to a volume which is sufficient to ignite the gaseous fuel, and to provide cooling and lubrication for various combustion chamber components.
A variety of dual fuel systems for diesel engines have heretofore been known in the art. For example, the Fox U.S. Pat. No. 3,540,419; Haidvogel U.S. Pat. No. 4,753,424; Akeroyd U.S. Pat. No. 4,463,734; Wolters U.S. Pat. No. 4,517,928 and Tanaka U.S. Pat. No. 4,603,674 are representative of such dual fuel systems. The heretofore known dual fuel systems typically include automatic load sensitive fuel controls which simultaneously modulate a supply of diesel fuel and a high pressure supply of gaseous fuel to provide, in combination, the varying total energy input requirements of a diesel engine. These combination fuel control systems customarily operate using what may be termed "predictive logic" wherein highly sophisticated electronics are utilized to monitor the engine's dynamic load, and to adjust (increase/decrease) the fuel input to the engine. More specifically, the dual fuel control calculates the theoretical energy requirements of the engine at a given load, and while restricting diesel fuel supply to minimum, delivers gaseous fuel through the engine intake manifold to a degree which is sufficient to maintain the engine output at a predetermined speed. Although these systems are fairly accurate at predicting the theoretical energy requirements of the engine, experience has proven that an engine equipped in this manner is relatively slow to react to the introduction of gaseous fuel. A delay in response time can cause incorrect fuel mixtures and combustion irregularities, such as improper fuel detonation, excessive combustion cylinder temperatures, excessive exhaust emissions, and rapid engine wear. Other potential drawbacks typically encountered with these systems include the need for an elevated gas supply pressure, a relatively high number of system components which may be subject to wear and failure, and costly installation and maintenance fees.
As a result of the hereinabove described problems, the applications of these types of fuel control systems are usually limited to situations where rapid transient response is not critical. It is pointed out that reaction time in an electric power generator is critical because fluctuations in engine speed cause fluctuations in the frequency of the electric power, which can ultimately cause damage to electrical devices being powered by the generator. Therefore, fuel systems for diesel electric generators are usually limited to diesel fuel only because of the slow reaction time of gaseous fuel.